If any US investigators 'pointed fingers' at ISI, then they need their heads examined. What does it mean to 'point fingers'? That someone alleged something? Sure, so what? Bring credible evidence, build a prima facie case before wasting ISI's time. Random accusations without corroborating evidence means zilch. Without legal follow through, all this 'finger pointing' is just media posturing for propaganda purposes.
As for Kasab's accomplices, the OP has explained the situation very well. From day ONE, India has been far more interested in playing politics and using this event to attack Pakistan than to solve the criminal case in good faith. Pakistan has been denied first-hand access to evidence and is being asked to conduct a very serious investigation by remote control.
It is true that, due to political expediency, India's shenanigans have been supported by the West, but the fact remains that the primary stumbling block to resolving the full criminal landscape has always been India, not Pakistan.